Computerized tomography (CT) apparatus has been employed recently to produce an image of a slice of an object, by constructing such an image with a computer, using either X-ray absorption data or NMR signals, which are obtained in a variety of projective directions in order to obtain an image of the desired slice of the object.
While producing a tomographic image of, for example, an abdomen of an animal utilizing such CT apparatus, a resultant image appears to be indistinct or blurred due to a shift in the position of the internal organs resulting from the respiration or the like of the object. In particular, in the nuclear magnetic resonance diagnostic apparatus (to be referred to as the "NMR-CT" hereinafter), when conducting tomographic imaging of the abdomen, chest, etc. of a human body, the resulting images noticeably appear to be blurred due to the influence of the respiration during the length of the time period, usually several minutes, which is necessary to collect the projection data in the various directions in a slice of the object.
Due to the foregoing problem, this invention devises an apparatus which combines the NMR-CT with a respiration synchronizing device. This combination operates by collecting the projection data in a slice of an object to be examined in synchronization with, for example, a breathing period corresponding to the respiration characteristic curve. This invention next produces an image using the collected projection data in the various projective directions. As a result, a more distinct image is formed which has almost no blur since the projection data is collected with the same phase time as the respiration cycle of the object.
In the prior art, a respiration synchronizing device has been available as a so-called impedance method wherein a respiration characteristic curve is obtained from the variations in the object impedance due to respiration while conducting minute high frequency current through the object.
In utilizing the above-described conventional respiration synchronizing device, however, the NMR-CT magnetic field is disturbed by another magnetic field which is generated at the time of flowing a current through the object, thereby making it impossible to detect NMR signals, since the NMR-CT is an apparatus utilizing an NMR phenomenon with an extremely uniform magnetic field.
Alternatively, a method employing a respiration meter might be devised as the respiration synchronizing device. A respiration meter measures the breathing volume of a human body through its mouth or nose, and as such, some of the instruments must be attached to the proper position on the face, thereby making the meter inconvenient.
Up to now, there has not been in existence a respiration synchronizing device that is suitable for an NMR-CT.